The Host-Mediated Assay and in vitro assays employing microsomal enzyme activation systems will be used to investigate the genetic activity of a series of chemicals. The test chemicals will consist of demonstrated mutagens and carcinogens requiring metabolic transformation to active forms. A series of bacterial and yeast indicator cells will be used in the assays to detect the formation of genetically active metabolites through measurements of mutation, mitotic recombination, mitotic gene conversion, and chromosomal nondisjunction induction. These studies will be used to further study the relationship between genetic and neoplastic activities of chemicals, and to provide base-line data necessary in the development of screening procedures for identification of potentially hazardous environmental chemicals.